Thanks Simon,
i think list of lists and tuples are good enough for me.
sage: R.<a,b> = FreeAlgebra(QQ, 2)
> sage: p = a*(a+2*b)
> sage: list(p)
> [(2, a*b), (1, a^2)]
>
is there a simple way to reverse this last step?
just for information - i asked this same question at the sympy mailing list
and i give below parts of the answer which would be important for people
using sage -
The parts below are from the replies of Aaron S. Meurer (asmeu...@gmail.com)
-
> Just a heads up, starting in the next release, symbols('xy') will create
one symbol named xy, not two symbols x and y. To get around this, you
should do symbols('x y') or symbols('x, y') (this works in the older release
too, so you can start to change your code now).
> In [9]: x, y = symbols('x y', commutative=False)
> In [10]: a = expand((x + y)**3)
> In [11]: a
> Out[11]:
> 2 2 3 2 2 3
> x⋅y⋅x + x⋅y + x ⋅y + x + y⋅x⋅y + y⋅x + y ⋅x + y
> In [12]: a.subs(x*y, y*x + 1)
> Out[12]:
> 3 2 2 3
> x⋅(1 + y⋅x) + x + y⋅x + y⋅(1 + y⋅x) + y ⋅x + y + (1 + y⋅x)⋅x + (1 +
y⋅x)⋅y
> Actually, it looks like if you are using SymPy 0.6.7, there is a bug that
makes this return a wrong result:
For people using sympy in sage, this last point seems important. I actually
checked and we use SymPy 0.6.4
Rajeev
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